Art of producing lubricating oils



Jan. 19, 1943. H. s. CHASE EFAL- 2,308,490

' .ART OF PRODUCING LUBRICATiNG o n s Filed Jan 17, 1936 GASOLINEPRESSED WAX DISIILLATE llllllll KERQSE-NE ueur GAS 01L 7 wAx msmuns.

CRUDE v DILUTION NAPHTHA KEROSENE 4 GAS on. LIGHT GAS OIL WAX DISTILLATEugHr LUBRICATING OIL DEWAXED BRIGHT sTocK SOLUTION I GASOLINE INVENTORS'f/grberf 5. a-se George C. Came 'WTTORNEY Patented Jan. 19, 1943 UNITEDSTATES "PATENT OFFICE ART or PRODUCING LUBRICATING OILS Herbert S.Chase, Elizabeth, and George C. Caine,

Bayonne, N. J., ass'ignor, by mesne assignments, of three-fourths toTide Water Associated Oil Company, NewYork, N. Y., a corporation ofDelaware Application January 17, 1936 Serial No. 5 $l,506

"ultimate oils as to characteristics such as gravity,

flash, viscosity, and the like, together with-[re fining problemsencountered in the processing of each broad fraction, necessitatescareful control of the primary crude distillation. A restrictivelimitation is imposed upon the proportions of This invention relates toimprovements in the acteristics necessary or desired for particular"lubricating services. More particularly, the in vention is concernedwith the manufacture of relatively light lubricating oils, of the typecommonly designated as neutral oils when derived from certain paraflinbase crudes as of Pennsylvania origin. It is an important objective ofthe invention to obtain such lubricating oils in greatly increasedyield, while avoiding impairment of desired properties either in theseor heavier-- lubricating oils concurrently produced from the same orother crude source. A further object-is the attainment of the foregoingobjective without creating difliculties in the operation of saryconventional refining steps.

As one embodiment of established commercial j value, the inventionconvenientlymay be illustrated in its application to the production ofcrudes of other than Pennsylvania origin. It 1 is to be clearlyunderstood, therefore, that no limitation is intended to be expressed orimplied;- in the particular selection of illustrative exneceswaxdistillate and ofcylinder stock which can be segregated from a givencrude; and thus it has not been possible heretofore to materiallyincrease the yield of neutral oil from a particular crude withoutcreating refining difficulties and impairing the quality of the brightstock concurrently produced.

According to the present invention, it hasnow been discovered that theforegoing difficulties can be obviated by a novel and efiectiveimproveamples and embodiments to' demonstrate the operative significanceof the invention.

In order to make available a complete range 0 motor oils by blendinglight and heavy lubricating oils in various proportions, the primarydis-' cylinder stock. In this manner, there is made available sourcematerial both for light lubricat ing oils (neutrals) and for heavylubricating oils (bright stocks). The production of these two sourcematerials to required specifications in the ment in the processing of awax distillate I (or other light or distillate lubricating stockfraction when crudes of other than Pennsylvania origin form the crudesource material) to neutral or similar light lubricating oils. Moreparticularly, such wax distillate, after dewaxing and other desiredrefining treatment, herein is subjected to a secondary fractionaldistillation in the presence of a relatively minor proportion ofhydrocarbon material having characteristics of a lubricatingstock andfurther characterized by a viscosity substantially higher than that ofthe finished neutral oil to be produced. As a specific example of suchmaterial may be mentioned bright stock produced concurrently from thecrude source supplying the wax distillate in process.

In the accompanying drawing, in which like reference characters denotelike parts,

Figure I depicts an illustrative flow sheet of a crude processing andrefining system for the production of lubricating oils, in whichprovision is made for incorporating the improvements con-' stituting thepresent invention; and,

Figure II is a partial flow sheet illustrating the application of theinvention to a somewhat difierent system for the production of lubricating oils. Referring now more particularly to Figure I,

the invention first will be illustrated in respect of its application tothe production of neutral oils in increased yield from a paraflin basePennsylvania crude. In such a system, primary distillation of the crudeis effected in the unit comprising a usual pipe still i andfractionating column 2. Gasoline is taken overhead, while otherlightiractions comprising kerosene and light gas oil are removed atsuitable points in the upper portion of the tower. A conventionallubricat ing or wax distillate is produced as a side out from a lowerintermediate point in the coluumn 2, and the tower bottoms comprise theresidual or cylinder stock fraction of the crude.

This primary distillation is carefully controlled according to usualpractice to yield cylinder stock bottoms having characteristics ofgravity, viscosity, and the like necessary for the ultimate productiontherefrom of bright stock meeting prescribed specifications. Theprocessing of cylinder stock to bright stock may, as indicated in theaccompanying flow sheet, involve the steps of dilution with naphtha tofacilitate subsequent handling, filtration thru decolorizing clay,centrifuge dewaxing, and reduction by distillation to remove the naphthadiluent.

The wax distillate, which forms the source material for ultimate neutraloil production, comprises the less viscous lubricating oil fractions ofthe original crude supply together with a relatively large amount of gasoil. It has a viscosity at 100 F. ordinarily somewhat under 100 Sayboltseconds as compared with corresponding neutral oil viscosities of 150Saybolt seconds and higher. This distillate lubricating stock first maybe dewaxed by any desired method suitable for the economic removal ofcrystalline wax as, for example, with the aid of the plate and framepresses indicated at 3 in the flow sheet, and then must be reduced by asecondary distillation wherein gas oil is taken overhead under suchconditions of tower control as to give a residual or bottoms fraction ofsuitable flash point and viscosity. The final processing of thisfraction ordinarily involves decolorizing by filtration through fullersearth or similar medium; and also may include such auxiliary refiningoperations as acid treatment, solvent extraction, and the like.

In a procedure such as the foregoing, the objects and advantages of thepresent invention are attained by a novel and improved method ofeffecting the secondary distillation or fractionation of the dewaxedlight lubricating stock fraction. Heretofore, it'has been customary topass this pressed or otherwise dewaxed distillate through a heating coil4 to a tower 5 wherein it is subjected to simple fractionation for theproduction of overhead gas oil and bottoms neutral stock. According tothe invention, this conventional procedure is modified by arranging forthe secondary fractional distillation to be conducted in the presence ofcertain hydrocarbon material brought into the system at a suitable pointand in minor proportion relative to the amount of pressed distillateavailable. The so improved secondary fractionation is carried out underconditions of tower control effective to give a neutral oil bottomsfraction meeting prescribed specifications of viscosity and flash point,and it has been found that the method of the invention givesunexpectedly beneficial results in the way of greatly increased yieldsof neutral oil product.

The invention contemplates the use of rather a wide variety ofhydrocarbon materials in connection with the improved method ofconducting the aforesaid secondary distillation of light lubricating oilstock. Desirably, the material selected will have lubricating stockcharacteristics, and in the preferred application of this phase of theinvention a suitably refined stock is regarded with favor. Thus, brightstock, obtained by filtering and dewaxing cylinder stock bottoms from aprimary distillation of parafiin or mixed base crude, serves verysatisfactorily in the instant process. Bright stock for this purposemay, in the case of Pennsylvania and certain Mid-Continent crudes, bederived from the same original petroleum source material as produce thedistillate lubricating stock fraction in process. Alternatively, thebright stock or other hydrocarbon material used equally well may bederived from extraneous sources. Likewise, it is feasible to usecylinder stock bottoms from various sources whether or not refined,heavy lubricating oil fractions fromvarious operations, selectedfractions of overhead cylinder stock or long residuums, and the like.

An important consideration in the selection of a particular petroleumfraction or other hydrocarbon material, to be introduced into thesecondary distillation or fractionation of light lubricating stock ashereinbefore described, is its viscosity. Quite viscous material ispreferred, and in any event the viscosity in question shouldbematerially higher than that of the finished neutral or other lightlubricating oil to be produced. By way of illustration, secondarydistillation of pressed wax distillate for the production of neutral oilhaving a final viscosity of the order of 180 Saybolt seconds at 100 F.was effectively enhanced as to yield when conducted in the presence ofbright stock in minor proportion having'a viscosity of the order of 2000Saybolt seconds at 100 F. This particular example is, of course, by nomeans limitative either in respect of the particular embodiment nowbeing described or of other applications of the invention. Thus, brightstock of higher and of somewhat lower viscosity than that just referredto likewise proved wholly satisfactory in meeting the requirements ofthe invention.

The desired substantial yield increases obtained in the practice of thepresent invention may be occasioned 'by the use of bright stock or othersuitable hydrocarbon material in relatively minor proportion based onthe amount of pressed distillate or other lubricating oil stockundergoing the improved secondary distillation or fractionation.Excessive proportions must be avoided as tending to impair suchproperties of the finished product as flash point. but considerablefreedom is permitted in selecting the proportion of such materialrelative to pressed distillate for any particular operation. In generalvery satisfactory results have been obtained with relative proportion ofthe order of 5% bright stock and pressed wax distillate, thesepercentages being by volume. For a particular operation, either in thisor other applications of the invention, the specific relativeproportions selected will be governed by such factors as the type orcharacter of the distillate stock undergoing secondary distillation orfractionation, the source and character of the additional hydrocarbonavailable or selected for use according to the invention, thespecifications to be met in the finished neutral or other lightlubricating oil product, and the production or yield increase desired.Thus, additional hydrocarbon material may be present during thesecondary distillation of pressed wax distillate or lubricating oilstock in proportions both lower and higher than 5% with effectiveenhancement of yield over that characterizing a like distillationwithout the presence of such material. It is not desired. therefore, tolimit the scope or contemplated application of the invention toparticular ratios or proportions.

Specific evidence of the operative significance of the present inventionis provided by'the results presented hereinbelow which were obtained incomparative runs using in one instance conventional procedure and in theother a method acspecification on the said neutral oil productwas 420 F;minimum. The charge to one such secondary distillation consisted of 100parts of pressed wax distillate; and the charge to a comparativesecondary distillation, utilizing the improvement of the presentinvention, consisted-of 96 parts of pressed wax distillate and 4 partsof a Pennsylvania bright stock having a viscosity 100 F. of the order of2000-2500 seconds Saybolt.

In the conventional run, the charge of 100 parts of pressed waxdistillate yielded 47 parts of bottoms neutral oil having an A. P. I.gravity of 29.8, a flash point (open cup) of 425 F. and a viscosity 100F. of 191 seconds Saybolt. The overhead fraction comprising theso-called gas oil or diluent components of the charge comprised 53parts.

In the run according to the present invention, the charge of 96 parts ofpressed waX distillate and 4 parts of bright stock yielded 59.8 parts ofbottoms neutral oil having an A. P. I. gravity of 30.3, a flash point(open cup) of 420 F. and a viscosity 100 F. of 189 seconds Saybolt. Theoverhead fraction comprising the so-called gas oil or diluent componentsof the charge comprised 40.2 parts.

Referring still to the accompanying flow sheet in Figure I, and to theproduction of neutral oils from paraflin base Pennsylvania crudes insuch a system according to the invention, the bright stock or otherhydrocarbon material may be introduced into the pertinent part of thesystem with some degree of freedom as to the point or method ofintroduction. In the flow sheet there is indicated diagrammatically aline 5 provided with a control valve '5 and connecting with the chargingline 8 through which pressed wax distillate enters the heating coil 4 ofthe secondary distillation unit. According to one method of practicingthe invention, bright stock or similar- 1y functioning material is fedthrough the line 6 into the line 8 where it meets and mixes with presseddistillate for continued flow therethrough in the coil 4. The flow ofbright stock through the line 6 is so regulated as to give desiredproportions of bright stock and pressed distillate, and after heating tosuitable temperature the mixture is passed to the tower 5 from whichneutral oil stock is withdrawn as a bottoms fraction of predeterminedviscosity and flash point.

Alternatively the added bright stock or like material may be introducedthrough a line 9 provided with a valve l0 and connecting into the outletor discharge line H from the heating coil 4f- In this instance, brightstock'in predetermined proportion mixes with the stock undergo secondarydistillation unit. Such procedures'ometimes may be desirable in theinterests of avoiding possible deleterious effects which might resultfrom subjecting the added material directly to heating in the coil 3.

Still a further method of practicing the invention comprises theintroduction of bright stock or the like through a line I2 provided witha valve i3 and leading into the upper portion of the, tower orfractionating column 5. Here the introduced material functions as anauxiliary reflux supply, this modification having particular advantagein that the added viscous hydrocarbon material is effectivelycontactedwith the rising lighter fractions of the lubricating stockundergoing secondary distillation or fractionation and thereby isenabled to function with marked efficiency in occasioning the balancedviscosity effect apparently contributing to the yield increases madeavailable by the present invention'without impairment of prescribedproduct characteristics.

The foregoing illustrative methods of practicing the invention are in nosense limitative thereof, and other alternatives which will be suggestedthereby to those skilled in the art are considered within the scopethereof. Likewise, it is contemplated that the foregoing and othermethods of operation may be used in various combinations to achieve thebenefits and advantages arising from the improved fractionaldistillation of light lubricating oil stock in the presence of suitablehydrocarbon material according to the invention;

Referring now to Figure II of the accompanying drawing, in the systemthere illustratively depicted a usual pipe still I and fractionatingcolumn 2 provides a distillation unit for the primary fractionation ofthe crude to yield fractions a indicated. A wax distillate (or. similarlubricating distillate when crudes of different origin are beingprocessed) is removed as an intermediate side out from the column 2 andpasses through the line l5 directly, without intervening dewaxing orlike refining treatment,

to a fractionating unit comprising a flash tower It. If desired steammay be supplied to the tower l 4 by suitable means (not shown) in or derto aid in the separation therein of light ends such as gas oil. Suchdiluent components of the Wax or lubricating. distillate pass overhead(together with steam) from the flash or re-fractionating tower M and arereturned to the column 2 as shown. Light lubricating oil, comprising theless viscous lubricating oil fractions of the original crude supply, isdrawn from the bottom of the tower, as a residual product havingpredetermined flash point and viscosity, and thereafter may besubjected, to ;such subsequent refining as may be necessary'ordesirable. Such refining will depend, among other factors, upon thecharacter of the original crude supply, as for example the necessity fordewaxing which may be effected by any suitable or effective method, thisand other subsequent refining operations forming no part of the presentinven tion.

In an operation such as the foregoing the yield of light lubricatingoil, withdrawn as a bottoms fraction from the flash fractionator I i,may be markedly increased while still meeting prescribed specificationsof viscosity and flash point by conducting such fractionation in thepresence of bright stock or similar functioning hydrocarbon materialaccording to the invention. Herein, provision is made for introducingsuch material to the fractionating unit or operation by two illustrativealternative methods, it being understood other methods suggested therebymay be used as well as various combinations which may be desirable inparticular commercial operations.

Thus, the invention in this embodiment may be practiced with efiectiveresults by the introduction of viscous hydrocarbon material through aline [6 provided with a control valve 6?; In this practice, theintroduced material enters the upper portion of the tower l4 andfunctions as an auxiliary reflux supply after the manner and with theadvantages previously discussed in connection with the use of line l2leading to column in Figure I. Alternatively, bright stock or the likemay be. introduced through. a line It provided with a control valve [9and serving to conduct the introduced material directly into the line [5through which the lubricating stock passes into the tower M. In thispractice the viscous hydrocarbon material is brought into the operationin intimate admixture with the stock undergoing re-fraetionation.

While the invention thus far has been described with particularreference to the production of neutral oils from parafiin base crudes ofPennsylvania origin, other embodiments are equally within itscontemplated scope and production. Broadly, the novel distillationmethod may be ap plied with advantage to the fractionation of anylubricating oil stock or fraction from which a relatively lightlubricating oil product is to be obtained by the controlled removal ofdiluent components such as gas oil. More specifically may be mentionedlight lubricating stock fractions derived from Mid-Continent, Texas,Coastal,

or other crudes regardless of the general crude processing procedure bywhich such fractions are obtained. As regards the Pennsylvania neutraloils, hereinbefore discussed at greater length, the two most generallymarketed products are those having viscosities at 100 F. of the order of150 Saybolt seconds and of 180 Saybolt seconds respectively. Certainother light lubricating oils such as those obtained from someMid-Continent crudes are produced with viscosities at 100 F. rangingfrom 100 seconds to 500 seconds. Similarly from other crudes, lightlubricating oil products may have market specifications within thisrange as well as higher and lower Saybolt viscosities at 100 F. It willbe understood, therefore, that no particular or special class of lightlubricating oil products is contemplated as the limitative objective ofprocess of the invention.

The increased light lubricating oil yields resulting from the practiceof the present invention have particular economic significance in thatthese increased yields are obtained with the aid of but minorproportions of heavier stock such as bright stock, cylinder stock, andthe like. Viewed in its commercial aspect, an outstanding benefit of theinvention, therefore, resides in the materially increased yield of totalmotor or other lubricating oil which is now made possible from a givencrude petroleum supply. As an example of this efiect may be consideredthe production of motor oils from a parafiin base crude as ofPennsylvania origin. Prior to the invention, the processing of such acrude for the eventual production of motor oils would yield a certainrelatively fixed proportion of bright stock and concurrentl a certainrelatively fixed proportion of neutral oil of given viscosity. With theapplication of the present invention to such an operation, the brightstock yield is but slightly reduced while theneutral oil yield for agiven viscosity is very materially increased; and thus the total yieldof motor oil from the crude has been enhanced without impairment ofquality in either the heavy or light lubricating oil products. Furtheradvantage, in this connection, resides in the flexibility which theinvention imparts to the general procedure since the yield increases maybe varied somewhat by varying the relative proportion of bright stock orlike functioning material introduced into the secondary distillation orfractionation of the stock from which the neutral oil product isderived. It will be understood, of course, that while in general largerproportions of introduced bright stock or the like occasion greaterneutral or other light lubricating oil yield increases, the relativeproportion of added material for any given operation must be selectedwith due regard to the necessity of meeting prescribed specifications inthe finished product such as fiash point.

In the various illustrative embodiments and examples herein, the neutralor other lubricating oil product obtained in increased yield accordingto the invention generally has been referred to and indicated as aresidual or bottoms fraction drawn from the improved fractionating ordistilling operation. In some circumstances of contemplated operation itmay be desirable to obtain such product as a side-cut withdrawn from thefractionating column at a suitable point in the lower portion thereof,rather than as a strictly bottoms or residual fraction. The expressionsbottoms fraction or residual product, as applied to lubricating oilproduct obtained by the invention, therefore is to be considered asembracing the practice just outlined as well as other equivalentpractice in this respect.

We claim:

1. In a process for recovering lubricating oil from a normally liquidhydrocarbon mixture containing relatively light lubricating componentsand lighter diluent components by fractionally distilling said mixtureto remove diluent components as distillate material and to recover lu-.bricating components as residual product fraction comprising arelatively light lubricating oil stock characterized by a particularviscosity and flash point, the improvement which comprises increasingthe yield of said relatively light lubricating oil stock recovered fromsaid mixture by conducting such fractional distillation of said mixturein the presence of a small proportion of heavy lubricating oil stockhaving a viscosity substantially higher than the viscosity of saidresidual product fraction, and selecting the proportion of said heavylubricating oil stock in amount sufficient to occasion more than anadditive increase in yield of said residual product fraction butinsuflicient to efiect appreciable deviation from the aforesaidparticular viscosity and flash point, the viscosity and fiash point ofsaid increased yield of relatively light lubricating oil stock beingsubstantially the same as that characterizing the relatively lightlubricating oil stock recovered in the absence of said additional heavyoil.

2. In a process for recovering a specified lubricating oil from anormally liquid hydrocarbon mixture comprising a distillate fractionderived from a petroleum source material and containing relatively lightlubricating components and lighter diluent components, which processincludes the steps of fractionally distilling the said mixture, removingdiluent components as distillate material, and recovering lubricatingcomponents as residualproduct fraction comprising a-relatively lightlubricating oil stock characterized by a particular viscosity and flashpoint, the improvement which comprises increasing the yield of saidrelatively light lubri-' cating oil stock as such residual productfraction having the aforesaid particular viscosity and crease in yieldofsaid residual product fraction but insufficient to cause appreciabledeviation from the aforesaid particular viscosity and flash point, theviscosity and flash point of said increased yield of relatively lightlubricating oil stock being substantially the same as thatcharacterizing the relatively light lubricating oil stock recovered inthe absence of said additional heavy oil.

3. A process for producing lubricating oil which includes subjecting apetroleum source material containing lubricating oil components tofractional distillation, separating therefrom a lower fractioncontaining relatively heavy lubricating oil components undiluted withlight non-lubricating oil components and a distillate intermediatefraction containing relatively light lubricating oil components and anappreciable amount of lighter diluent components, passing saidintermediate fraction to a subsequent distillation stage, fractionallydistilling the same and recovering therefrom as residual productfraction a relatively light lubricating oil stock characterized by aparticular viscosity and flash point, and increasing the yield oflubricating oil stock having the aforesaid particular viscosity andflash point above the amount of lubricating oil stock of substantiallythe same viscosity and flash point that is obtainable from saidintermediate fraction in the absence of additional heavy lubricating oilcomponents by conducting said last referred to fractional distillationin the presence of a small proportion of heavy lubricating oil stockhaving a viscosity substantially higher than the viscosity of saidresidual product fraction, selecting the proportionate amount of saidheavy lubricating oil stock to be small as compared with the amount ofheavy lubricating oil components in said lower fraction but sufiicientto occasion more than an additive increase in yield of said residualproduct fraction, the viscosity and flash point of said increased yieldof relatively light lubricating oil stock being substantially the sameas that characterizing the relatively light lubricating oil stockrecovered in the absence of said additional heavy oil.

4. A process for producing lubricating oil which includes subjecting apetroleum source material containing lubricating oil components tofractional distillation, separating therefrom a lower fractioncontaining relatively heavy lubricating oil components undiluted withlight non-lubricating oil components and a distillate intermediatefraction containing relatively light lubricating oil components and anappreciable amount of lighter diluent components, passing saidintermediate fraction to a subsequent distillation stage, fractionallydistilling the same and recovering therefrom as residual product mediatefraction in the absence of additional heavier hydrocarbon oilcomponentsbyconducting said last referred to fractionaldistillation in Ithe presence of a small proportion of hea'vy lubricating oil componentsfrom said lower fraction, said proportion being so selected as tooccasion more than an additive increase lnj yield of said residualproduct fraction; the viscosity and flash point of saidincreased yieldof relatively light lubricating oil stock being substantially the sameas that characterizing the relatively light lubricating oil stockrecovered in the absence of said additional heavy oil.

5. Process of producing from a wax-containing crude petroleum,lubricating oil in distinct portions comprising relatively lighter andheavier product fractions each meeting predetermined specificationsincluding viscosity and flash point, which comprises subjecting suchpetroleum to a primary distillation and fractionation to segregateselected fractions thereof, Withdrawing a residual fiaction comprisingrelatively heavy lubricating oil stock of predetermined viscosity,refining and dewaxing said residual fraction to produce therefrom alubricating 011 comprising the said relatively heavier product portionof the process, separately withdrawing a distillate fraction comprisingrelatively light lubricating oil stock having a viscosity substantiallyless than that of the lubricating oil to be obtained therefrom as therelatively light product portion of the process, passing said distillatefraction to a dewaxing stage, withdrawing therefrom a dewaxed distillatefraction having a substantially lower viscosity and flash point than thesaid relatively lighter product portion of the process, passing saiddewaxed distillate fraction to a secondary fractional distillationstage, concurrently passing a small proportion of said relativelyheavier lubricating oil product to said secondary distillation stage,conducting said secondary fractional distillation, withdrawing therefroma residual fraction comprising relatively light lubricating oil stockhaving predetermined viscosity and flash point, and refining said lastmentioned residual fraction to produce therefrom a lubricating oilcomprising the said relatively lighter product portion of the process;said process being particularly characterized by a greater total yieldof lubricating oil, in distinct relatively lighter and heavier portionseach meeting predetermined specifications of viscosity and flash point,than is obtained when the same said product portions are producedwithout the step of passing heavy lubricating oil to the said secondarydistillation stage.

6. Process of producing from a wax-containing crude petroleum,lubricating oil in distinct portions comprising relatively lighter andrelatively heavier product fractions each meeting predeterminedspecifications including viscosity and flash point, which comprisessubjecting said petroleum to a primary distillation and fractionation tosegregate selected fractions thereof, withdrawing a residual fractioncomprising relatively heavy lubricating oil stock of predeterminedviscosity, refining and dewaxing said residual fraction to producetherefrom a lubricatfraction a relatively light lubricating oil stock 7mg oil comprising the said relatively heavier product portion of theprocess, separately withdrawing a distillate fraction comprisingrelatively light lubricating oil stock having a viscositysubstantiallyless than that of the lubricating oil to be obtained therefrom as therelatively light product portion of the process, passing said distillatefraction to a dewaxing stage, withdrawing therefrom a dewaxed distillatefraction having a substantially lower viscosity and flash point than thesaid relatively lighter product portion of the process, passing saiddewaxed distillate fraction to a secondary distillation stage,concurrently passing to said secondary distillation stage a smallportion of viscous hydrocarbon material derived from the residualfraction of said primary fractionation, conducting said secondaryfractional distillation, withdrawing therefrom a residual fractioncomprising relatively light lubricating oil stock having predetermined-viscosity andfiash point, and refining said last mentioned residualfraction to produce therefrom a lubricating oil comprising saidrelatively lighter product portion of the process; said process beingparticularly characterized by a greater total yield of lubricating oil,in distinct relatively lighter and heavier portions each meetingpredetermined specifications of viscosity and flash point, than isobtained when the same product portions are produced without the step ofpassing viscous hydrocarbon material to said secondary distillationstage.

HERBERT S. CHASE. GEORGE C. CAINE.

